Snap action mechanism



Aug. 9,1949. T. G. RICHMOND 2,478,503

' SNAP-ACTION MECHANISM Filed April 8, 1947 4 Sheets-Sheet 1 d5 TGliiclnmozzd 1949- T. cs. RICHMOND 2,478,503

SNAP-ACTION MECHANISM Filed April 8, l947 4 Sheets-Sheet 2 a Ire/ v ezvol ('z'Glficizzzzozzd g- 1949- T. G. RICHMOND 2,473,503

SNAP-ACTION MECHANISM Filed April 8, 1947 4 Sheets-Sheet 5 1949- T. G. RICHMOND 2,473,503

SNAP-ACTION MECHANISM Filed April 8, 1947 4 Sheets-Sheet 4 l'zzuezziofi & IGJiziaZzmwuZ UNITED STATES PATENT OFFICE SNAP ACTION MECHANISM Thomas Guthrig Richmond, Glasgow, Scotland, assignor of one-half to Robert Maclaren & Company Limited, Glasgow, Scotland Application April 8, 1947, Serial No. 740,068 In Great Britain April 23, 194.6

9 Claims. (Cl. 297-15) This invention has reference to snap action mechanism and is particularly suitable for use in combination with a heat sensitive device so that it functions as a thermostat to make and break an electric circuit, or to operate a valve but is not restricted to such applications.

The present invention has for its object to provide an improved snap action mechanism of a simple, cheap and compact construction.

Another object of our invention is to provide an improved snap action mechanism which can be easily adjusted as may be desired to control the size of the gap.

A still further object of the invention is to provide improvements in snap action mechanism whereby adjustment can be readily made to regulate the force necessary to operate the said mechanism.

The invention will now be described with reference to the annexed drawings wherein:

Figure 1 is a sectional elevation of a thermostatically operated switch having one form of snap action mechanism in accordance with the invention.

Figure 2 is a plan view thereof.

Figure 3 is an inverted plan view thereof.

Figure 4 is a section on the line 4-4 of Figure 1, and

Figure 5 is an end elevation looking to the left.

Figure 6 is a sectional elevation of another form of snap action mechanism in accordance with the invention.

Figure '7 is a sectional end elevation thereof, and

Figure 8 is a plan View thereof.

Figures 9, 10 and 11, Figures 12, 13 and 14, Figures 15, 16 and 17, Figures 18, 19 and 20, Figures 21, 22 and 23 are all views corresponding to Figures 6, 7 and 8 of further constructions of snap action mechanisms in accordance with the invention.

In the drawings like reference letters denote the same or corresponding parts.

In all the snap action mechanisms illustrated a designates a resilient flexed operating member which is maintained in a state of compression by a second flexed resilient supporting member b.

The thermostatically operated switch shown in Figures 1 to 5 comprises a body 0 of porcelain or other insulating material to the upper face of which is secured by means of screws 0 a bridge piece 0 Clamped between the bridge piece and the body are the two sides of a resilient plate of metal or other suitable material which is slotted as at c to form the resilient flexed member a which is held in a state of compression, and, at

the two sides thereof the flexed resilient member I). This member b is maintained flexed by the plate bearing at one end thereof on a protuberance c projecting from the upper face of the body and by an adjustable screw 0 threaded through a nut c seated on a shoulder c".

Said protuberance c and screw 0 are located on the longitudinal centerline of the plate which latter is, in consequence bowed transversely as indicated at 0 This transverse bowing gives a more decided snap action, and causes snap action before the centre of the member a reaches the plane containing its ends.

Said bridge piece extends over one side of the body as at c and carries one of the terminals 0 of the switch.

Extending centrally below the body is a plate at through which is threaded a screw d which is locked by means of a lock nut d Said plate is secured to the body by means of screws d and at its outer end is upwardly turned as at d*, said end carrying the other terminal C1 The upper end of said screw d constitutes a fixed contact and a movable contact 11 which cooperates therewith is carried by the centre of the resilient flexed member a. An adjustable stop or contact in the form of a screw d", which is threaded through the bridge piece and is locked by means of a lock nut d is provided to restrict the movement of the moveable contact. That is, said stop controls the size of the gap between the fixed and moveable contacts. This adjustment may be also carried out as required by screw d The size of the aforesaid gap is of micro dimensions, i. e. between .002 and .020 inches, the size being controlled by adjustment of the screw (1".

To the base of the body is secured a bi-metallic element e which is anchored at one end by means of a bolt and unt e and bearing on the other end of said member is a temperature regulating plunger e slidable vertically within a cylindrical casing e and loaded by means of a helical compression spring e This casing is screwed within an enclosing cylindrical sleeve e which is supported by a bracket 2 secured by means of a bolt and nut e to a pillar c at one end of the body.

Extending through a hole 1 in the body is a switch operating plunger f of insulating or other material which, at its upper end bears on the resilient flexed member a towards one end thereof and at its lower end on the bi-metallic element e at a point remote from the end by which it is secured to the body by the bolt e The flexed resilient member a is continually in a state of compression as the two ends thereof are anchored to the ends of the flexed member b. The degree of compression in which the member a. is maintained, and therefore its resistance to movement, is governed by the fiexure of the flexed member I). The flexure in the latter can be regulated as desired by adjusting the screw Also the pressure necessary to operate the snap action mechanism can be regulated by more or less loading the spring loaded plunger e such regulation being effected by screwing the casing c more or less into the fixed sleeve e In Figure 1 the moveable contact d is shown in contact with the fixed contact al so that the electric circuit is completed from terminal d through plate d, fixed contact al snap action mechanism, bridge piece 0 and terminal 0 When the bi-metallic element e becomes distorted under the action of heat it applies pressure to the plunger f and when such pressure becomes suificiently great the flexed member a will snap past its dead centre thereby separating the moveable from the fixed contacts and thus interrupting the circuit.

This movement of the flexed member a is restricted by the adjustable stop or contact cl which may be so adjusted that when the pressure of the plunger f is removed the mechanism will not snap back to its initial position or so adjusted, that is the gap between the contacts, when opened, is reduced, that on the pressure of the said plunger being removed the mechanism will snap back. Such automatic reversal can only be obtained when the actuating force is of a resilient nature. In the switch described the bi-metallic element imparts a resilient pressure on the plunger.

If desired the protuberance c in lieu of being a fixture may be in the form of an adjustable stop by which the flexure in the place a can be regulated in like manner to the screw 0 In the snap action mechanism shown in Figures 6 to 8 the flexed member a is held in a state of compression by means of a cage formed of two superimposed flexed plates g and g both having a rectangular opening 9 cut therein but the opening in the upper plate being extended at its two ends over the under plate and narrowed so as to form a rebate to accommodate the ends of the flexed member a and prevent lateral movement of the member a. In such mechanism the flexed plates constitute the second flexed resilient member b. The operation of this construction of snap action mechanism is similar to that described.

The construction shown in Figures 9 to 11 differs from that shown in Figures 1 to 5 in that the centre member of the slotted plate is anchored to the body member 0 by the bridge piece 0 This central member constituting the flexed member b serves to maintain the two sides of the slotted plate in a state of compression, said two sides thereby constituting a double flexed member a. This double member carries two moveable contacts which co-operate with two fixed contacts. The operation of this snap action mechanism is similar to that above described.

In the construction of snap action mechanism shown in Figures 12 to 14 the resilient plate is slotted to form two central resilient tongues or leaves, the inner ends of which are clamped to the body 0 by the bridge piece, said tongues constituting the flexed member I). The two sides of the plate are connected at their centre which carries the moveable contact d. The operation of this mechanism is similar to that described with reference to Figures 1 to 5.

The snap action mechanism shown in Figures 15 to 17 is very similar to that described with reference to Figures 1 to 5 but the flexed member a is not continuous but is formed of two blades or leaves interconnected by an interconnecting member 11 to which is clamped the inner end of one of the blades or leaves as at h while the inner end of one of the blade or leaf makes a knife edge contact with said member as at W. Two moveable contacts are carried by said member, there being two fixed contacts 11 and two adjustable stops or contacts (1 The construction of snap action mechanism illustrated in Figures 18 to 20 is similar to that just described with the exception that the inner ends of the two blades or leaves constituting the flexible member a both make knife edge contacts with the connecting member h.

Likewise the construction shown in Figures 21 to 23 is similar to that shown in Figures 15 to 17 with the difference that the inner ends of the two blades or leaves constituting the flexible member a are both clamped to the connecting member h carrying the moveable contacts.

If desired in all arrangements the flexed member or one or more of them may be in the form of bi-metallic strips so that they will flex in one direction or another when subjected to changes in temperature, such flexing being either suflicient to effect the snap action or alternatively sufflcient to modify the force required to operate the mechanism.

I claim:

1. Snap action mechanism embodying a resilient supporting member maintained in a longitudinally bowed state, a longitudinally flexed operating member carried by the supporting member and maintained thereby in a state of compression, and means by which the ends of the supporting member are maintained in a transversely bowed state, such transverse bowing being transmitted to the operating member and diminishing to zero towards the transverse centre line, the construction and arrangement being such that the operating member functions with a sharp snap action when a force is applied thereto suificient to force the transverse centre thereof short of the plane containing its extremities to an extent of microdimensions.

2. Snap action mechanism embodying a resilient plate slotted longitudinally to form interconnected strips, a supporting body, means by which at least one of the strips is clamped transversely to said body, means by which said plate is bowed longitudinally so that at least one strip not so clamped is permanently maintained in a state of compression and means by which said plate is bowed transversely at each end thereof, such transverse bowing diminishing to zero towards the centre, the construction being such that the strip maintained under compression functions with a sharp snap action when a force is applied thereto sufhcient to force the transverse centre thereof to within microdimensions of the plane containing its ends.

3. Snap action mechanism embodying a resilient plate slotted longitudinally to form interconnected strips, a supporting body, means by which at least one of the strips is clamped transversely to said body, stops carried by the supporting body and on which the ends of said plate bear and by which the said plate is bowed longitudinally so that at least one strip not so clamped is permanently maintained in a state of compression and by which the plate is bowed transversely at each end thereof, such transverse bowing diminishing to zero towards the centre, the construction being such that the strip maintained under compression functions with a sharp snap action when a force is applied thereto sufiicient to force the transverse centre thereof to within microdimensions of the plane containing its ends.

4. Snap action mechanism embodying a resilient plate slotted longitudinally to form interconnected strips, a supporting body, means by which at least one of the strips is clamped transversely to said body,tops, at least one of which is adjust- ,able, carried by the supporting body and on which the ends of said plate bear and by which the said plate is bowed longitudinally so that at least one strip not so clamped is permanently maintained in a state of compression and by which the plate is bowed transversely at each end thereof, such transverse bowing diminishing to zero towards the centre, the construction being such that the strip maintained under compression functions with a sharp snap action when a force is applied thereto sufficient to force the transverse centre thereof to within microdimensions of the plane containing its ends, adjustment of the stop effecting the sensitivity of the action.

5. Snap action mechanism embodying a resilient supporting member maintained in a longitudinally bowed state, a longitudinally flexed operating member carried by the supporting member and maintained thereby in a state of compression, means by which the ends of the supporting member are maintained in a transversely bowed state, such tranverse bowing being transmitted to the operating member and diminishing to zero towards the transverse centre thereof, an adjustable stop to restrict the movement of the flexed operating member and means by which a resilient operating force is applied to said member to effect the snap action, adjustment of said stop enabling the snap action mechanism to be adjusted so that it will auto-v matically resume its normal position when the operating force is removed.

6. Snap action mechanism embodying a resilient plate slotted longitudinally to form interconnected strips, a supporting body, means by which at least one of the strips is clamped transversely to said body, means by which said plate is bowed longitudinally so that at least one of the strips not so clamped is bowed longitudinally and maintained in a state of compression, means by which said plate is bowed transversely at each end thereof, such transverse bowing being transmitted to the member maintained under compression and diminishing to zero towards the transverse centre, an adjustable stop to restrict the movement of said member and means by which a resilient operating force is applied to said member to effect the snap action, adjustment of said stop enabling the snap action mechanism to be adjusted so that it will automatically resume its normal position when the operating force is removed.

7. A thermostatic device embodying a res lient supporting member maintained in a longitudinally bowed state, a longitudinally flexed operating member carried by the supporting member and maintained thereby in a state of compression, means by which the ends of the supporting member are maintained in a transversely bowed state, such transverse bowing being transmitted to the operating member and diminishing to zero towards the transverse centre thereof, and means sensitive to heat and which applies a force normal to said member, which latter functions with a sharp snap action when the means sensitive to heat applies a force thereto sufficient to force the transverse centre thereof to within microdimensions of the plane containing its ends.

8. Snap action mechanism embodying a slotted plate maintained in a longitudinally flexed state, a flexed member fitted into said slot and maintained by said plate in a state of compression, and means by which the ends of the plate are maintained in a transversely bowed state, which transverse bowing is transmitted to the said member and diminishes to zero towards its transverse centre, and means by which said member can be distorted so that it will function with a sharp snap action when the centre thereof is moved to within microdimensions of the plane containing its ends.

9. Snap action mechanism embodying a resilient supporting member maintained in a longitudinally flexed state, a longitudinally flexed operating member carried by the supporting member and maintained thereby in a state of compression, at least one of said members being bimetallic, and means by which the ends of the supporting member are maintained in a transversely bowed state, such transverse bowing being transmitted to the operating member and diminishing to zero towards the transverse centre line, the construction and arrangement being such that the operating member functions with a short snap action when an internal force in the bi-metallic member forces the centre of the operating member short of the plane containing its ends to an extent of microdimensions.

THOMAS GUTHRIG RICHMOND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,215,665 Landis Feb. 13, 1917 1,668,974 Mottlau May 8, 1928 1,669,531 Mottlau May 15, 1928 2,413,130 Aitken Dec. 24, 1946 2,429,812 Hausler Oct. 28, 1947 FOREIGN PATENTS Number Country Date 8,229 Australia Apr. 17, 1928 364,189 Great Britain Jan. 7, 1932 

